This present invention relates to a pneumatic tire for passenger cars and more particularly to tires for racing and similar very light performance uses.
Conventionally tires have a symmetrical tread profile when considered in cross-section to show the curvature in the radial plane.
Proposals have been made to use different tread compounds at either side of the tire for improving wet grip and to use different tread pattern groove layouts at either side of the tread to provide some asymmetry. The latter also gives increased pattern density on the outside half of the tire to improve cornering when that part of the tire is carrying most of the cornering forces. However, there is a reduction in the tire's wet grip ability due to poorer drainage.
Conventional tires use dual radii tread profiles. The central region of the tread has one large radius and the shoulders have a second substantially smaller radius. This is to provide a wider flatter tread with a more uniform contact patch to the road. Japanese Patent publication 3271003 proposed an asymmetrical profile shape in which the outer part of the tread of the tire, when fitted to a vehicle, has a smaller radius than the inner part to allegedly improve the wet grip ability of the tire.
U.S. Pat. No. 4,763,708 proposes that the transverse sectional plane has a maximum outer diameter point spaced axially from the central plane of the tread and the radius of curvature of the narrower side is greater than the other side to improve the resistance to abrasion of the shoulder regions.
It has also been proposed to stiffen the inboard sidewall of the tire so that more load is carried by that sidewall to offset some of the load transfer during cornering. However, but the bulk of the material in the stiffened sidewall increases heat generation leading to durability problems.
However the above tires do not optimize contact patch load distribution while cornering and thus lateral grip and handling are not optimized and uneven wear occurs. Furthermore for high cornering powers known tires are very wide which increases cost and leads to installation problems on vehicles. Another proposal provides a pneumatic tire having a tread region which has a profile, when considered in transverse cross-section of a new tire terminating at the sides of the tread in inner and outer shoulder regions respectively, wherein each said shoulder region has a shoulder drop, which is the distance in the radially inward direction from the point of maximum tire diameter to a shoulder point at the edge of the shoulder region, wherein when the tire is mounted on its scheduled rim and inflated to its scheduled pressure the tread region is asymmetric having its point of maximum tire diameter offset in the axial direction of the tire from the center line of the tire section in the direction of the inner shoulder edge, and the shoulder drop of the outer shoulder is greater than the shoulder drop of the inner shoulder such that the tread region has an asymmetrical profile.
Such a tire provides a substantial improvement in vehicle handling but still further improvements in handling and also in fatigue performance are desired.